The major objective is to determine the audiological features of age-related hearing loss and to provide an empirical basis for diagnosis, rehabilitation, and prevention. The general strategy is to complete similar experiments on aging humans and aging gerbils. Some of the experiments test the applicability of the gerbil as an animal model of human presbyacusis. Other experiments are designed to assess age-related declines in auditory function such as frequency selectivity, and to identify locations within the auditory system that may be affected by the aging process. The experiments on frequency selectivity include studies of evoked potentials in humans and animals, and psychophysical masking and distortion product emissions in humans.